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Next: <a href="Register-Classes.html#Register-Classes" accesskey="n" rel="next">Register Classes</a>, Previous: <a href="Type-Layout.html#Type-Layout" accesskey="p" rel="prev">Type Layout</a>, Up: <a href="Target-Macros.html#Target-Macros" accesskey="u" rel="up">Target Macros</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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<a name="Register-Usage"></a>
<h3 class="section">18.7 Register Usage</h3>
<a name="index-register-usage"></a>

<p>This section explains how to describe what registers the target machine
has, and how (in general) they can be used.
</p>
<p>The description of which registers a specific instruction can use is
done with register classes; see <a href="Register-Classes.html#Register-Classes">Register Classes</a>.  For information
on using registers to access a stack frame, see <a href="Frame-Registers.html#Frame-Registers">Frame Registers</a>.
For passing values in registers, see <a href="Register-Arguments.html#Register-Arguments">Register Arguments</a>.
For returning values in registers, see <a href="Scalar-Return.html#Scalar-Return">Scalar Return</a>.
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<tr><td align="left" valign="top">&bull; <a href="Register-Basics.html#Register-Basics" accesskey="1">Register Basics</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Number and kinds of registers.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Allocation-Order.html#Allocation-Order" accesskey="2">Allocation Order</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Order in which registers are allocated.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Values-in-Registers.html#Values-in-Registers" accesskey="3">Values in Registers</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">What kinds of values each reg can hold.
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<tr><td align="left" valign="top">&bull; <a href="Leaf-Functions.html#Leaf-Functions" accesskey="4">Leaf Functions</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Renumbering registers for leaf functions.
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<tr><td align="left" valign="top">&bull; <a href="Stack-Registers.html#Stack-Registers" accesskey="5">Stack Registers</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Handling a register stack such as 80387.
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